Which of the following reactions do not result in the preparation of potassium dichromate?
(I) `4FeCr_2O_4+8 Na_2CO_3+7O_2to`
(II) `Na_2CrO_4+H_2SO_4 to `
(III) `Na_2Cr_2 O_7 + 2KCl to `

Options

A. I and II
B. II and III
C. I and III
D. I, II, and III

Explanation

To determine which of the given reactions do not result in the preparation of potassium dichromate (K2Cr2O7), we will analyze each reaction step by step.

### Step 1: Analyze the First Reaction
The first reaction is:
\[ 4 \text{FeCr}_2\text{O}_4 + 8 \text{Na}_2\text{CO}_3 + 7 \text{O}_2 \to 8 \text{Na}_2\text{CrO}_4 + 2 \text{Fe}_2\text{O}_3 + 8 \text{CO}_2 \]

- In this reaction, iron chromite (FeCr2O4) reacts with sodium carbonate (Na2CO3) and oxygen (O2) to produce sodium chromate (Na2CrO4) and other products.
- **Conclusion**: This reaction produces sodium chromate, not potassium dichromate.

### Step 2: Analyze the Second Reaction
The second reaction is:
\[ 2 \text{Na}_2\text{CrO}_4 + \text{H}_2\text{SO}_4 \to \text{Na}_2\text{Cr}_2\text{O}_7 + \text{H}_2\text{O} \]

- Here, sodium chromate (Na2CrO4) reacts with sulfuric acid (H2SO4) to form sodium dichromate (Na2Cr2O7) and water.
- **Conclusion**: This reaction produces sodium dichromate, not potassium dichromate.

### Step 3: Analyze the Third Reaction
The third reaction is:
\[ \text{Na}_2\text{Cr}_2\text{O}_7 + 2 \text{KCl} \to \text{K}_2\text{Cr}_2\text{O}_7 + 2 \text{NaCl} \]

- In this reaction, sodium dichromate (Na2Cr2O7) reacts with potassium chloride (KCl) to produce potassium dichromate (K2Cr2O7) and sodium chloride (NaCl).
- **Conclusion**: This reaction results in the preparation of potassium dichromate.

### Final Conclusion
From the analysis of the three reactions:
- The first reaction does not produce potassium dichromate.
- The second reaction also does not produce potassium dichromate.
- The third reaction does produce potassium dichromate.

Therefore, the reactions that do not result in the preparation of potassium dichromate are:
**(I) and (II)**.

### Answer:
The correct answer is: **(I) and (II)** do not result in the preparation of potassium dichromate.

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